1. Field of the Invention
The present invention relates to an optical pumping-type solid-state laser apparatus with a semiconductor laser device, in which the solid-state laser is optically pumped by a laser beam with a predetermined wavelength emitted from the semiconductor laser device so as to generate a laser beam with a target wavelength.
2. Description
A conventional solid-state laser is optically pumped by light emitted from a flash lamp so as to generate a laser beam. In general, however, many solid-state lasers such as Nd-doped YAG lasers efficiently absorb light with only a short range of wavelengths. Since the light emitted from the flash lamp has a wide variety of wavelengths, only a small part of the light thereof is absorbed by the solid-state laser. Thus, this type of solid-state laser has low efficiency of conversion of light from the light source into a final laser beam.
On the other hand, laser light emitted from a semiconductor laser device has a similar range of wavelengths to that of the light efficiently absorbed by the solid-state laser mentioned above. Thus, the use of such a semiconductor laser device as a light source for optical pumping attains higher efficiency in the conversion of the light from the light source into a final laser beam. With the development of a more reliable semiconductor laser device of higher output power, an optical pumping-type solid-state laser apparatus which utilizes a semiconductor laser device as a light source for optically pumping the solid-state laser for the generation of a desired laser beam has been developed.
FIG. 5 shows a conventional optical pumping-type solid-state laser apparatus with a semiconductor laser device. The semiconductor laser device 61 is mounted on a temperature regulator 67, which modifies the wavelength of the laser light to be emitted from the semiconductor laser device 61. The laser beam emitted from the semiconductor laser device 61 is directed through a light-converging unit 62 onto a light-receiving facet 63a of a YAG rod 63. At the other side of the YAG rod 63 is disposed a reflecting mirror 64, facing a light-emitting facet 63b of the YAG rod 63. The light-receiving facet 63a of the YAG rod 63 and the reflecting mirror 64 constitute a laser resonator. The YAG rod 63 absorbs laser light emitted from the semiconductor laser device 61 and is optically pumped by the laser light so as to generate a laser beam with a wavelength of 1.064 .mu.m.
FIG. 6A shows the light-absorption characteristics of the YAG rod 63 with respect to wavelengths of light. As shown in FIG. 6A, the YAG rod 63 absorbs light with a wavelength of 0.809 .mu.m at high efficiency. Thus, the semiconductor laser device 61, which can emit a laser beam with the wavelength of 0.809 .mu.m, is used for optically pumping the YAG rod 63.
The light-receiving facet 63a of the YAG rod 63 is coated with a film which transmits light with a wavelength of 0.809 .mu.m and reflects light with a wavelength of 1.064 .mu.m. On the other hand, the light-emitting facet 63b facing the reflecting mirror 64 is coated with a film which transmits light with the wavelength of 1.06 .mu.m. The surface of the reflecting mirror 64 which faces the light-emitting facet 63b is coated with a reflecting film for reflecting light with the wavelength of 1.064 .mu.m at a high reflectivity.
In such an optical pumping-type solid-state laser apparatus, the temperature regulator 67 regulates the temperature of the semiconductor laser device 61 so that the laser light to be emitted therefrom has the wavelength of 0.809 .mu.m, which can be absorbed by the YAG rod 63 at high efficiency as described above. Thus, the laser beam emitted from the semiconductor laser device 61 is efficiently absorbed by the YAG rod 63, which is then optically pumped by the laser light to generate therein a laser beam with a wavelength of 1.064 .mu.m. Then, the resultant laser beam is emitted therefrom at a high output level. An optical pumping-type solid-state laser apparatus with the above configuration has been developed as a small-sized laser light source for laser instrumentaion and measurement, laser material processing, and the like.
In the semiconductor laser device 61 used in such a conventional optical pumping-type solid-state laser apparatus, mode hopping or the like may arise due to deterioration with time, changes in temperature or in the level of the injected current, and the like. This changes the wavelength of the laser light emitted from the semiconductor laser device 61. Although a semiconductor laser device which can output a laser beam with a desired wavelength is carefully selected, the wavelength thereof tends to change for the above-mentioned reason, and accordingly deviates from the short range of wavelengths of light which can be absorbed at high efficiency by the YAG rod 63. This deviation changes the amount of the laser light to be absorbed by the YAG rod 63, thereby changing the resultant optical output power of the solid-state laser apparatus.
The laser generation efficiency of an Nd-doped YAG rod 63 with respect to the wavelengths of the laser light emitted from a semiconductor laser device 61 is shown in FIG. 6B. As shown in FIG. 6B, when the wavelength of the laser light deviates from the short range of wavelengths including 0.809 .mu.m, the output level of the resultant laser beam is greatly decreased. As described above, the laser light of the semiconductor laser device used in the conventional optical pumping-type solid-state laser apparatus is likely to change in wavelength, which naturally decreases the output level of the resultant laser beam, thereby preventing the solid-state laser apparatus from generating laser light in a stable manner for a long period of time.